U.S. patent number 4,865,587 [Application Number 07/220,615] was granted by the patent office on 1989-09-12 for syringe and catheter apparatus.
Invention is credited to Peter T. Walling.
United States Patent |
4,865,587 |
Walling |
September 12, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
Syringe and catheter apparatus
Abstract
To inflate the balloon element on the distal end of a pulmonary
artery catheter an improved gas syringe is provided which is both
volume and pressure-limited so that the syringe is capable of
discharging into the catheter no more than the maximum design gas
inlet volume thereof while at the same reducing the maximum
attainable pressure within the catheter to a predeterminable level
substantially below that reached when a conventional volume-limited
syringe of the same gas discharge capacity is used. The syringe
volume delivery limitation is achieved by forming rearwardly
disposed plunger stop members, or a suitable vent opening, in a
sidewall portion of the syringe body. The pressure limitation is
obtained by forming a pressure absorption zone which defines a
substantially inextensible enlargement of the gas-receiving
interior of the catheter. In an alternate embodiment of the
syringe, an orifice plate having a small orifice opening therein is
secured across the syringe outlet to limit the balloon inflation
rate during an initial portion of the operation of the syringe.
Inventors: |
Walling; Peter T. (Dallas,
TX) |
Family
ID: |
21703995 |
Appl.
No.: |
07/220,615 |
Filed: |
July 18, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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3075 |
Jan 14, 1987 |
4795431 |
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Current U.S.
Class: |
604/97.02;
604/208; 604/920 |
Current CPC
Class: |
A61M
25/104 (20130101); A61M 25/10182 (20131105); A61M
2205/3368 (20130101); A61M 2025/09008 (20130101) |
Current International
Class: |
A61M
25/10 (20060101); G61M 025/00 () |
Field of
Search: |
;604/97,99,208,210,121
;128/349 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Inflating Characteristics of Swan-Ganz Catheter Balloons: Clinical
Considerations-Jean Francois Hardy, MD & Taillefer, M.D. .
A Study of the Lateral Wall Pressure Exerted by Balloon-Tipped
Catheters, Burdick, M.D., and Willians, M.D. .
Pathophysiology of Rupture of the Pulmonary Artery by Pulmonary
Artery Balloon-Tipped Catheters, Hardy, MD, Morissette MD,
Taillefer MD and Vauclair, MD. .
Pressure-Volume Relationships of the Pulmonary Artery Catheter
Balloon-McDonald & Zaidan-Oct. 1982-18 pages. .
Pressure-Volume Relationships of the Pulmonary Artery Catheter
Balloon-McDonald & Zaidan-Feb. 25, 1983-4 pages. .
American Edwards Soft-Wedge Syringe-Descriptive and Evaluation
Materials-1982-4 pages..
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Primary Examiner: Pellegrino; Stephen C.
Attorney, Agent or Firm: Hubbard, Thurman, Turner &
Tucker
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. application Ser.
No. 003,075 filed on Jan. 14, 1987 now U.S. Pat. No. 4,795,431..
Claims
What is claimed is:
1. Improved syringe and catheter apparatus comprising:
catheter means for internally blocking a body passage, said
catheter means being adapted to internally receive a predetermined
maximum volume of pressurized gas from a source thereof and having
an inflatable portion insertable into the body passage for
inflation therein by the pressurized gas received within said
catheter means;
syringe means operable to discharge up to said predetermined
maximum volume of pressurized gas through an outlet of said syringe
means into the interior of said catheter means;
pressure reducing means carried by said syringe means defining an
essentially inextensible enlargement of the gas-receiving interior
of said catheter means, said enlargement functioning as a pressure
absorption zone which reduces to a predetermined magnitude the
maximum internal pressure within the gas receiving interior of said
catheter means caused by receipt therein of said predetermined
maximum volume of pressurized gas from said syringe means so that
said predetermined maximum volume of pressurized gas may be forced
into and retained within the gas-receiving interior of said
catheter means without creating therein a pressure exceeding said
predetermined magnitude thereof; and
orifice means operatively associated with said outlet of said
syringe means for limiting the initial pressurization rate of said
inflatable portion of said catheter means during an initial portion
of the operation of said syringe means.
2. The apparatus of claim 1 wherein:
said syringe means include a hollow syringe body and said pressure
absorption zone is disposed within said body.
3. The apparatus of claim 2 wherein:
said syringe means further include a plunger disposed in said
hollow syringe body and operative to force gas therein outwardly
through said outlet, and
said pressure reducing means include stop means, positioned within
said hollow syringe body between said plunger and said outlet, for
engaging and stopping said plunger in a spaced relationship with
said outlet during movement of said plunger toward said outlet.
4. The apparatus of claim 3 wherein:
said stop means define an internal enlargement of said hollow
syringe body.
5. The apparatus of claim 4 wherein:
said internal enlargement is positioned adjacent said outlet.
6. The apparatus of claim 4 wherein:
said internal enlargement is spaced apart from said outlet.
7. The apparatus of claim 3 wherein:
said stop means comprise a hollow stop member disposed within said
hollow syringe body.
8. The apparatus of claim 1 wherein:
said syringe means include a hollow syringe body and said pressure
absorption zone is external to said hollow syringe body.
9. The apparatus of claim 8 wherein:
said catheter means have a gas inlet, and
said pressure absorption zone is interposed between said outlet and
said gas inlet.
10. The apparatus of claim 9 wherein:
said pressure reducing means comprise tube means, interconnectable
between said outlet and said gas inlet, for defining said pressure
absorption zone.
11. The apparatus of claim 1 wherein:
said syringe means include a hollow syringe body having an internal
volume greater than said predetermined maximum volume of
pressurized gas, said outlet being formed in said hollow syringe
body, and a plunger received in said hollow syringe body and
operative to force gas therein outwardly through said outlet,
said apparatus further comprise volume limiting means carried by
said hollow syringe body for limiting the volume of gas
dischargeable by said plunger through said gas outlet to said
predetermined maximum volume of pressurized gas.
12. The apparatus of claim 11 wherein:
said hollow syringe body has a sidewall portion, and
said volume limiting means comprise an opening formed through said
sidewall portion and spaced apart from said outlet.
13. The apparatus of claim 11 wherein:
said hollow syringe body has a sidewall portion, and
said volume limiting means define an inward enlargement of said
sidewall portion positioned to engage and stop said plunger during
movement thereof away from said outlet.
14. The apparatus of claim 1 wherein:
said orifice means include a plate member secured to and extending
across said outlet of said syringe means, said plate member having
an orifice opening extending therethrough.
15. A syringe for use in internally pressurizing a catheter,
comprising:
a hollow body adapted to receive a quantity of gas and having a
hollow outlet end portion operatively connectable to the catheter
for discharging gas thereinto from within said body;
a plunger received in said body for movement toward and away from
said outlet end thereof to respectively discharge gas through said
outlet end and draw gas into said body;
pressure reducing means for limiting the pressure increase within
the catheter to a predetermined magnitude when a predetermined
maximum volume of gas is forced into the catheter from said
syringe, said pressure reducing means including stop means,
interposed between said plunger and said outlet end of said body,
for engaging and stopping said plunger in a spaced relationship
with said outlet end during movement of said plunger toward said
outlet end; and
orifice means carried by said hollow body for limiting the initial
pressurization rate within the catheter during an initial portion
of the operation of said syringe.
16. The syringe of claim 15 wherein:
said stop means comprise a hollow stop member disposed within said
body of said syringe.
17. The syringe of claim 16 wherein:
said stop member is adjacent said outlet end portion of said body
of said syringe.
18. The syringe of claim 16 wherein:
said stop member has a generally cylindrical configuration and is
coaxially disposed within said body of said
19. The syringe of claim 18 wherein:
said stop member is cross-sectionally smaller than the interior of
said body and has a laterally projecting portion formed
thereon.
20. The syringe of claim 19 wherein:
said laterally projecting portion is an annular flange.
21. The syringe of claim 20 wherein:
said annular flange is an end flange and is positioned adjacent
said outlet end portion of said body of said syringe.
22. The syringe of claim 15 wherein:
said stop means define an internal enlargement of said body of said
syringe.
23. The syringe of claim 22 wherein: said internal enlargement is
positioned adjacent said outlet end portion of said body of said
syringe.
24. The syringe of claim 22 wherein:
said internal enlargement is spaced apart from said outlet end
portion of said body of said syringe.
25. The syringe of claim 24 wherein:
said internal enlargement comprises a generally facing duality of
inwardly projecting wall portions of said body of said syringe.
26. The syringe of claim 15 wherein the internal volume of said
hollow body is greater than said predetermined maximum volume of
gas and said syringe further comprises:
volume limiting means, associated with said body of said syringe,
for cooperating with said plunger to limit the volume of gas
dischargeable through said outlet end portion of said body of said
syringe to said predetermined maximum volume of gas.
27. The syringe of claim 26 wherein:
said volume limiting means include an opening extending laterally
through a wall portion of said body spaced apart from said outlet
end portion thereof.
28. The syringe of claim 26 wherein:
said volume limiting means include stop means for limiting movement
of said plunger away from said outlet end portion of said body of
said syringe.
29. The syringe of claim 28 wherein:
said stop means are defined by an internal enlargement of said body
of said syringe.
30. The syringe of claim 29 wherein:
said internal enlargement comprises a generally facing duality of
inwardly projecting wall portions of said body of said syringe.
31. The syringe of claim 15 wherein:
said orifice means include a plate member secured to and extending
across said outlet end portion of said hollow body, said plate
member having an orifice opening extending therethrough.
32. The syringe of claim 31 wherein:
said plate member is disposed within said outlet end portion.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to medical devices, and
more particularly provides an improved syringe and inflatable
catheter apparatus which incorporates a uniquely configured volume
and pressure-limited gas syringe used to internally pressurize the
catheter portion of the apparatus.
Potential over-pressurization of inflatable catheter elements used
to internally block various body passages, such as the pulmonary
artery, is a well known and long-standing problem in the practice
of medicine. Pulmonary artery catheters are typically provided at
their distal end with a small balloon which is selectively
inflatable by a gas syringe connected to the catheter's
gas-receiving inlet. To utilize the catheter, a sheath element is
inserted into a suitable vein, such as the jugular vein, and the
distal end of the catheter is fed through the sheath into the vein.
When the distal end of the catheter exits the inner end of the
sheath, the balloon is inflated. The inflated balloon acts as a
"float" to assist in further insertion of the catheter by drawing
its distal end through the vein (by virtue of the blood flow
therethrough) and ultimately into a position in which the inflated
balloon becomes "wedged" in a branch of the pulmonary artery.
Lodged in a pulmonary artery branch in this manner the distal end
of the catheter may be utilized in a conventional manner to monitor
the pulmonary artery "wedge" pressure via the resulting pressure
trace pattern on an oscilloscope operatively connected to the
catheter.
After this initial wedge pressure reading is taken the balloon is
deflated, but the catheter is normally left in place so that the
balloon may be re-inflated to take subsequent wedge pressure
readings. The over-pressurization problem previously mentioned
typically arises when, between these intermittent balloon
inflations, the distal catheter end "migrates" into a smaller
portion or branch of the pulmonary artery. Subsequent balloon
inflation then takes place in an unintended arterial portion which
may be weaker and/or of a smaller interior cross-section than
anticipated. If great care is not exercised in re-inflating the
catheter balloon in these instances, the balloon can be
over-pressurized and cause the artery to burst.
Typically, the catheter has a design inlet gas volume capacity
corresponding to the gas volume required to fully inflate the
balloon. In a variety of conventional manners the syringe is
volume-limited to assure that no more than this designed-for gas
volume can be forced into the catheter from the syringe to thereby
prevent over-inflation of the balloon.
However, even with this volume "matching" between the syringe and
catheter it is possible to cause over-pressurization of the
catheter balloon during the intermittent reinflation thereof, and
concomitant rupture of the artery portion into which it has
migrated, if the syringe is not correctly and carefully used by its
operator. Specifically, during each subsequent reinflation of the
balloon the syringe plunger must be moved slowly toward the end of
its stroke within the syringe body to avoid inordinately high
"peak" pressures in the inflating balloon. Even the proper slow
movement of the syringe plunger can cause the balloon to rupture
the smaller or weaker artery portion if the plunger is pushed too
far and too hard by the syringe operator.
The operational safety of conventional pulmonary artery catheters
(as well as other types of syringe-operated inflatable catheters)
is thus to a large degree dependent upon the "feel" transmitted to
the syringe plunger as the catheter interior pressure is being
increased, and the syringe operator's skill in interpreting and
reacting to such "feel". Even though the pressure trace on the
catheter-connected oscilloscope will normally indicate when the
artery portion has been sufficiently occluded by the inflating
balloon (by generating a recognizable "wedge" pattern), certain
heart infirmities (such as an incompetent mitral valve) can
generate a potentially misleading trace pattern which, even though
the partially inflated balloon is fully blocking the artery
portion, indicates that further balloon inflation is needed. It is
this further balloon inflation which, in conventional
volume-limited syringe and catheter apparatus, can easily burst the
artery.
Various attempts have been previously made to eliminate this
over-pressurization problem. For example, as exemplified in U.S.
Pat. Nos. 3,642,005; 3,905,361 and 4,064,882 inflatable external
indicator balloons have been placed on non-inserted portions of
catheters to provide the syringe operator with an additional visual
indication of the degree of inflation reached in the internal
catheter balloon. Other supplemental visual internal catheter
pressure indicia, such as simple pressure gauges have also been
utilized. These and other visually oriented safety devices,
however, must (along with the oscilloscope trace pattern) be
continually watched by the syringe operator, and properly reacted
to, to be effective. Also particularly in the case of pressure
gauges, moving parts are involved which are always subject to
malfunction and wear.
Other mechanical devices, such as pressure relief valves, have also
been used to actually limit the pressure supplied to the catheter.
Illustrative devices of this type may be found in U.S. Pat. Nos.
3,871,374; 4,116,201 and 4,439,185. Other representative syringe
and catheter devices may be found in U.S. Pat. Nos. 4,335,723;
4,370,982 and 4,583,974. The problem with mechanical
pressure-limiting devices such as multi-component pressure
regulators or relief valves is that they are subject, like all
devices with moving parts, to malfunction or failure.
It can be seen from the foregoing that a longstanding need exists
for improved syringe and inflatable catheter apparatus having
greater operational safety from a catheter over-pressurization
standpoint. Accordingly, it is an object of the present invention
to provide such apparatus.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention, in accordance
with a preferred embodiment thereof, improved syringe and catheter
apparatus is provided which comprises a catheter having an
inflatable element such as a balloon on its distal end and an
improved gas syringe which is connectable to the catheter and
operable to inflate the distal end balloon thereon. The syringe is
uniquely provided with both volume and pressure limiting means
which cooperatively function to permit the syringe to force up to
the maximum design volume of pressurized gas into the catheter
while automatically reducing the maximum attainable gas pressure
within the catheter (and thus the balloon) to a predetermined level
well below that attainable when utilizing a conventional syringe
with the same maximum gas volume discharge capability.
The volume limiting means in the improved syringe of the present
invention are of generally conventional construction and may
comprise either rearwardly disposed plunger stops formed within the
syringe body to limit the rearward travel of the syringe plunger, a
rearwardly disposed vent opening formed through a sidewall portion
of the syringe body, or other suitable volume limiting means. In
any event, the volume limiting means function to assure that no
more than the maximum design gas volume of the catheter can be
forced thereinto from the syringe.
The pressure limiting or pressure reducing means in the improved
syringe function to create therein a pressure absorption zone which
defines a substantially inextensible enlargement of the
gas-receiving interior of the catheter. This volume enlargement
create, in effect, a "dead space" which reduces to a predetermined
level the pressure rise within the catheter associated with its
receipt of its design gas volume from the syringe. In the preferred
embodiment of the present invention the pressure limiting means
comprise forward stop means, disposed within the syringe body, for
engaging and stopping the syringe plunger during forward travel
thereof at a position spaced rearwardly from the forward end wall
of the syringe body. By limiting the forward movement of the
syringe plunger in this fashion the pressure absorption zone is
formed within a forward end portion of the improved syringe. In one
version of this improvement the forward stop means are defined by a
hollow cylindrical stop member coaxially disposed within a forward
end portion of the syringe body. In another version the forward
stop means are formed by diametrically opposed, radially inwardly
projecting sidewall portions of the syringe body which are spaced
rearwardly from the forward endwall of the body.
In an alternate embodiment of the present invention the forward
stop means are deleted from the syringe and the unique pressure
absorption zone is formed externally to the syringe by a length of
tubing operatively interconnected between the syringe outlet and
the gas-receiving inlet of the catheter and having an interior
volume equal to the desired volume of the pressure absorption
zone.
The present invention conveniently permits the conversion of a
standard syringe, having an internal volume greater than the design
volume of a particular catheter, to a volume and pressure-limited
syringe whose maximum dischargeable gas volume is precisely matched
to the maximum design inlet volume of the catheter while at the
same time reducing to a much safer, and predeterminable, level the
maximum pressure attainable within the catheter. This conversion is
easily and inexpensively achieved by simply forming the previously
described volume limiting means on the syringe body and
appropriately creating the pressure absorption zone either within
the syringe body via the forward stop means, or externally to the
body by using an appropriately sized length of interconnecting
tubing.
Importantly, the unique operational safety improvement provided by
the present invention is achieved without the addition of any
complex, moving or wear-prone mechanical parts to the syringe and
catheter apparatus such as mechanical pressure regulators, pressure
relief valves, pressure gauges or external balloon inflation
indicators. Moreover, other than the usual catheter-connected
oscilloscope, there is no need for supplementary visual
pressure-monitoring apparatus (such as pressure gauges or external
balloon elements) which must be carefully and continuously watched
by the syringe operator. All of these previously utilized
mechanical pressure-monitoring devices are uniquely eliminated in
the present invention due to its provision of the cooperating
volume limiting means and the pressure absorption zone.
In a further alternate embodiment of the present invention, a small
orifice plate is operatively mounted in the outlet passage of the
syringe. The orifice opening in such plate functions to reduce the
initial inflation pressure transmitted to the catheter balloon,
thereby reducing the initial inflation rate of the balloon, to
provide an added measure of safety to the overall balloon inflation
process.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially sectioned and exploded fragmentary side
elevational view of an improved syringe and catheter apparatus
which embodies principles of the present invention;
FIG. 1A is a partially sectioned side elevational view of a rear
end section of an alternate embodiment of the syringe portion of
the apparatus;
FIG. 2 is a perspective view of a hollow cylindrical
pressure-limiting member disposed within the syringe of FIG. 1;
FIG. 2A is a perspective view of an alternate embodiment of the
pressure-limiting member;
FIG. 3 is an enlarged scale cross-sectional view through the
syringe, taken along line 3--3 of FIG. 1, and illustrates the
pressure-limiting member of FIG. 2 disposed therein;
FIG. 3A is an enlarged scale cross-sectional view similar to that
of FIG. 3, but with the pressure-limiting member of FIG. 2A
disposed in the syringe;
FIG. 4 is an enlarged scale cross-sectional view through the
syringe taken along line 4--4 of FIG. 1;
FIG. 5 is a partially sectioned side elevational view of a forward
end portion of a further alternate embodiment of the syringe;
FIG. 6 is a partially sectioned and exploded fragmentary side
elevational view of an alternate embodiment of the syringe and
catheter apparatus;
FIG. 7 is a cross-sectional view through a front end portion of a
further alternate embodiment of the syringe having an inflation
rate-limiting orifice plate member operatively secured within its
outlet tube section;
FIG. 8 is an enlarged scale cross-sectional view through the outlet
tube section of the FIG. 7 syringe, taken along line 8--8 of FIG.
7; and
FIG. 9 is a graph illustrating representative intralumenal
pressure-time curves for a conventional syringe and catheter
apparatus, the improved syringe and catheter apparatus of FIG. 1,
and the improved syringe and catheter apparatus of FIG. 1 with the
orifice plate member of FIGS. 7 and 8 incorporated therein.
DETAILED DESCRIPTION
Depicted in FIG. 1 is an improved syringe and catheter apparatus 10
which embodies principles of the present invention and comprises a
pulmonary artery catheter 12, of conventional construction, and a
uniquely configured syringe 14 which is utilized in a manner
subsequently described to force air (or another, more readily
soluble gas such as carbon dioxide) into the catheter 12. The
representative catheter 12 illustrated in FIG. 1 is of the
"quadruple lumen" type having, at its proximal or inlet end, four
tubes or "lumens" 16, 18, 20, and 22 which are operatively
interconnected to a single insertion tube 24 by means of a suitable
connector fitting 26. Secured to the insertion tube 24, adjacent
its distal end 28, is a small latex balloon member 30 which is
inflatable to the dashed line configuration 30.sub.a in response to
the receipt of pressurized gas within the lumen 16 from the syringe
14. Pressurized syringe gas received within the lumen 16 is flowed
into the balloon 30 via an internal passage (not illustrated)
within the insertion tube 24 and a small slit 32 formed in the tube
24 and enveloped by the balloon.
At its outer end, the gas inlet or balloon inflation lumen 16 is
provided with an inlet fitting 34 having a gas inlet passage 36
flanked by a pair of small connecting tabs 38, and a gas shutoff
valve member 40 which is slidable relative to the balance of the
inlet fitting 34, as indicated by the double-ended arrow 41, to
selectively open and close the gas inlet passage 36. The other
three lumens 18, 20 and 22, which play no direct role in the
present invention, respectively comprise a proximal injection
lumen, a distal lumen, and a thermistor lumen. These three lumens
are utilized in a conventional manner to monitor various
characteristics within the pulmonary artery and right heart into
which the inflatable portion 24 of the catheter 10 is inserted as
subsequently described.
Syringe 14 has a hollow, transparent plastic body 42 of an
elongated cylindrical configuration. Body 42 has a forwardly
disposed, conical inner or outlet endwall 44, and an open rear or
outer end 46 having outwardly projecting finger support tabs 48
formed thereon. Extending axially outwardly from the forward
endwall 44, and communicating with the interior of the syringe body
42, is a reduced diameter, hollow cylindrical outlet tube 50.
Coaxially circumscribing the outlet tube 50 is a larger diameter
hollow cylindrical connection collar 52 which projects outwardly
from the endwall 44. The collar 52 is somewhat shorter than the
outlet tube 50 and is internally threaded as at 54.
The catheter 12 is connectable to the syringe 14 by inserting the
outlet tube 50 into the gas inlet passage 36 of the catheter inlet
fitting 34 so that the connecting tabs 38 enter the syringe
connecting collar 52. The syringe body 42 and the catheter inlet
fitting 34 are then relatively rotated so that the connecting tabs
38 engage the internal threads 34 to thereby releasably lock the
inlet fitting 34 to the connecting collar 52.
To pressurize gas within the syringe body 42 and force the gas into
the balloon inflation lumen 16, the syringe 14 is provided with a
plunger 56 which is coaxially received within the syringe body 42
for movement toward and away from the syringe body endwall 44 (as
may be seen by comparing the solid line position of the plunger to
its dotted line position 56.sub.a) to respectively force gas from
and draw gas into the syringe body. Plunger 56 has an elongated
plastic body portion 58 defined in cross-section by four
longitudinally extending transverse ribs 60 (see also FIG. 4). At
its outer end the plunger body 58 is provided with a circular thumb
flange 62, while at the inner end of the plunger body is a smaller
diameter circular flange 64. Secured to the inner end of the
plunger body 58, and abutting its inner end flange 64, is a rubber
seal element 66 which slidably and sealingly engages the interior
surface of the syringe body 42 and has a generally conically shaped
inner end portion 68 that is complementarily configured relative to
the endwall 44.
To utilize the syringe and catheter apparatus 10, the tube portion
24 thereof is inserted into and through a suitable vein, such as
the jugular vein, until the distal end 28 of the insertion tube 24
is properly positioned within the superior vena cava. The syringe
plunger 56 is then manually pushed toward the syringe body endwall
44 to inflate the balloon 30. Balloon 30 is then "floated" through
the heart and into the pulmonary artery until a branch thereof is
occluded by the inflated balloon. With a pulmonary artery branch
blocked in this manner, a variety of conditions therein, such as
the "wedge" pressure downstream from the distal tube end 28 may be
measured and monitored. This initial measurement and monitoring (as
well as subsequent measurement and monitoring) is effected by an
oscilloscope which is operatively associated with the catheter and
generates a trace pattern indicative of the arterial wedge pressure
downstream from the inflated balloon.
After this initial wedge pressure reading has been taken, the
balloon is deflated. However, the catheter is then normally left in
its inserted position so that the balloon can be selectively
reinflated to take subsequent wedge pressure and/or other readings.
It is primarily in conjunction with these subsequent balloon
inflations that the well-known problem of balloon
over-pressurization, and concomitant bursting of a pulmonary artery
branch can occur.
This problem can arise if, after the initial deflation of the
balloon, the distal catheter end "migrates" into an arterial branch
which is substantially smaller and/or weaker than the one the
inflated balloon initially became wedged in and occluded.
Subsequent inflation of the balloon in this smaller and/or weaker
arterial branch, if not done with extreme care, can easily cause
the arterial branch to rupture and cause very rapid death of the
patient.
Arterial catheters, such as the representative catheter 12 depicted
in FIG. 1, are typically designed (and so labeled) to receive up to
a predetermined maximum volume of pressurized air (or other gas)
from its associated syringe-such volume of gas being that which
will fully inflate the balloon 30 or other inflatable element
associated with the insertion tube 24. Subject to the expected
variations in interior sizes of pulmonary arteries, and the
strengths thereof, this overall volume design limitation is
intended to safely limit the maximum balloon pressure.
As an example, the illustrated catheter 12 has a 1.5 cc volume
design limitation. Typically, conventional syringes used in
conjunction with catheters of this type have an internal body
volume greater than the design volume of the catheter. This is due
to the fact that it is convenient, and less expensive, for the
apparatus manufacturer to utilize a single, standard-sized syringe
body with a variety of catheters having varying volume design
capacities. As an example, the syringe 14 depicted in FIG. 1 in
conjunction with the 1.5 cc catheter 12 has a nominal gas discharge
capacity of 5 cc-i.e., a gas discharge capacity substantially
larger than the design limit of catheter 12.
In an attempt to safely "match" the over-sized syringe to the
catheter, it has been conventional practice to provide the syringe
with volume-limiting means which function to limit the maximum gas
volume dischargeable therefrom to the nominal volume inlet capacity
of the catheter. In conventional over-sized catheter syringes, such
volume-limiting means are provided by forming in the side wall
portion of the syringe body laterally inwardly directed,
diametrically opposed projections 70 which are positioned forwardly
of the open body end 46 and rearwardly of the plunger body flange
64. The projections 70 are normally formed by pressing heated
cylindrical forming members against diametrically opposite sidewall
portions of the syringe body to plastically deform such sidewall
portions into the syringe body so that they project inwardly o the
periphery 72 (FIG. 4) of the plunger body flange 64. Positioned in
this manner, the inward projections 70 function as stop members
which limit the rearward travel of the plunger within the syringe
body.
In a conventionally constructed catheter syringe of this type,
these projections are axially positioned on the syringe body so
that the gas volume within the syringe body between the plunger
seal element and the outlet endwall of the body is equal to the
nominal volume capacity of the catheter. Thus, the dischargeable
gas quantity of the syringe is precisely matched to the design
volume capacity of the catheter. As illustrated in FIG. 1, this
volume-limiting technique, via the previously described stop
members 70, is incorporated into the improved syringe 14 of the
present invention. However, for reasons subsequently described, the
distance between the illustrated stop members 70 and the endwall 44
is greater than such distance in catheter syringes of conventional
construction.
A modified conventional volume-limiting technique is also
incorporated in the alternate embodiment 14.sub.a of the syringe 14
depicted in FIG. 1A, the syringe 14.sub.a being in all other
regards identical to the syringe 14. In the syringe 14.sub.a, the
rearwardly disposed plunger stop members 70 are eliminated, and are
replaced by a small vent opening 74 formed through the sidewall of
the syringe body forwardly of the open rear end 46 thereof. It can
be seen in FIG. 1A that with the plunger seal element 66 disposed
rearwardly (i.e., leftwardly) of the opening 74, forward motion of
the plunger 56 toward the opening 74 will not force pressurized gas
from within the syringe body into the catheter lumen 16. Instead,
such forward plunger motion will simply force gas from within the
syringe body outwardly through the vent opening 74.
It is only when the forwardmost annular sealing surface 76 of the
seal element 66 forwardly crosses the opening 74 that the plunger
can force pressurized gas outwardly through the outlet end of the
syringe and into the lumen 16. Accordingly, in conventional
catheter syringes, the vent opening 74 is axially positioned along
the length of the syringe body such that the volume between the
opening and the outlet endwall of the syringe body is equal to the
design volume capacity of the catheter. However, as in the case of
the rear stop members 70 in syringe 14, the opening 74 in syringe
14.sub.a is spaced a greater distance rearwardly from the endwall
44 than it would be in a conventional syringe having the same gas
discharge capacity.
In and of itself, however, neither of these conventional
volume-limiting means (or other similar volume-limiting means)
completely eliminates the potential problem of over pressurizing
the balloon 30 when it is disposed within an artery having a lesser
strength or internal dimension than anticipated when, for example,
the uninflated catheter has distally migrated. In these instances,
even though no more than the catheter design gas volume can be
forced thereinto from the syringe, over pressurization of the
catheter balloon, and arterial rupture, can occur.
Typically, upon each re-inflation of the catheter balloon the
syringe operator must carefully and slowly depress the syringe
plunger until the oscilloscope trace pattern indicates a "wedge"
condition has been achieved--i.e., the inflating balloon has
occluded the arterial branch in which it is lodged. At this point
(which normally occurs with the balloon in a partially inflated
condition) the syringe operator must desist from further inflating
the balloon.
However, as is well known, the configurations of both "normal" and
"wedge" trace patterns on the monitoring oscilloscope vary widely
from patient to patient and can occasionally mislead even
experienced syringe operators as to the existence of balloon
occlusion in the artery branch in which the balloon is disposed.
More specifically, the trace pattern may closely resemble one which
is normally indicative of a nonoccluded artery when, in fact, full
occlusion exists and further balloon inflation could rupture the
artery. As but one example, an incompetent mitral valve can
generate back pressure pulses which can misleadingly indicate that
the distal catheter end is still "free" within the artery even
though it is fully blocking the artery.
It is in these instances when great care must be exercised in
inflating the catheter balloon. The syringe operator must be
acutely aware of the resistance of the syringe plunger to further
forward travel and stop its further travel if too great a
resistance is encountered. In other words, the operator must rely
on the "feel" of the syringe plunger to safeguard against arterial
rupture because even in volume-limited syringes of conventional
construction excessive pressures can easily be generated within the
occluding balloon.
In a preferred embodiment thereof the present invention uniquely
and substantially reduces these potential balloon over
pressurization problems by providing within the body 42 of syringe
14 (or syringe 14.sub.a as the case may be) a stop member 80 which,
in conjunction with the volume-limiting means 70 (or 76) affords
the syringe the advantageous capability of being able to force into
the catheter 12 up to its designed-for maximum volume of
pressurized gas (to thereby fully inflate the balloon 30 during its
blood-drawn initial "float" through the heart) while at the same
time automatically reducing to a predetermined magnitude the
pressure within the balloon 30 when it receives this maximum volume
of gas from the syringe.
Referring to FIGS. 1-3, the stop member 80 has a hollow cylindrical
body 82 whose external diameter is somewhat smaller than the
internal diameter of the syringe body 42. At one end thereof the
body 82 is circumferentially enlarged to define an annular end
flange 84. The stop member 80 is coaxially disposed within a
forward end portion of the syringe body so that the flange 84 abuts
a radially outer portion of the conical endwall 44 and the opposite
annular end surface 86 of the stop member faces the plunger seal
element 66.
Interposed in this manner between the seal element 66 and the
syringe outlet tube 50, the stop member 80 creates within the
syringe body 42 a pressure absorption zone which defines an
essentially inextensible enlargement of the gas-receiving interior
of the catheter 12. Such pressure absorption zone comprises the
annulus 88 circumscribing the stop member body 82, the interior 90
of the body 82, and the generally conical space 92 disposed between
the flange 84 and the syringe body endwall 44. The end surface 86
of the stop member 80 engages and stops the plunger seal element 66
during forward movement thereof in a position (indicated at
66.sub.a in FIG. 1) spaced rearwardly from the syringe body endwall
44.
This end surface 86 is suitably spaced from the stop members 70 so
that when the plunger seal element 66 moves from its solid line
position to its dotted line position 66.sub.a a maximum of 1.5 cc
of pressurized gas (i.e., the maximum design volume of the catheter
12) is forced through the stop member interior 90 and the outlet
tube 50 into the lumen 16 and the insertion tube 24 to thereby
fully inflate the balloon 30.
However, since the total effective volume of the gas-receiving
interior of the catheter 12 is increased by the pressure absorption
zone volume created by the stop member 80, the resulting internal
pressure within the balloon 30 is reduced by a preselected
magnitude determined by the size of the stop member 80. By properly
selecting the maximum attainable pressure within the balloon 30, he
risk of rupturing an artery which is smaller or weaker than
anticipated is substantially reduced. Importantly, such risk is
effectively reduced without regard to how the plunger 56 is pushed
or who is pushing it.
The syringe 14.sub.a of FIG. 1A is functionally identical to the
syringe 14, in that it is both volume and pressure-limited, except
that the volume-limiting wall opening 74 does not form a rearward
mechanical stop for the plunger 56. Instead, as previously
described, it functions (together with the forward stop member 80)
to limit the "effective" stroke of the plunger since internal
pressurization of the syringe body does not begin until the sealing
surface 76 of the seal element forwardly traverses the wall opening
74.
It should be noted that the actual maximum stroke of the plunger 56
in syringe 14 (or the maximum "effective" plunger stroke in syringe
14.sub.a) necessary to discharge the maximum design gas volume into
the catheter 12 is at least somewhat longer than would otherwise be
necessary in the absence of the stop member 80. This is due to the
fact that the gas-receiving interior of the catheter 12 has been
effectively increased by the volume of the pressure absorption zone
defined by the stop member 80. Accordingly, more gas must be
displaced within the syringe body by the plunger seal element 66 to
flow the design volume of gas into the catheter, and the distance
between the stop members 70 (or the opening 74) and the endwall 44
is concomitantly increased. It will be appreciated that the
necessary spacing between the stop member end surface 86 and the
rear stop members 70, or the side-wall opening 74, is determined by
the total volume of the pressure absorption zone created by the
stop member 80.
It will be readily appreciated that the stop member 80 may be given
a variety of alternate configurations other than that depicted in
FIG. 2. As but one example of such alternate configuration, an
alternate forward stop member 80.sub.a (FIGS. 2A and 3A) may be
provided which has a hollow cylindrical configuration of an
external diameter just slightly smaller than the internal diameter
of the syringe body 42 so that the stop member 80.sub.a is closely
received in the syringe body adjacent its endwall 44 as
cross-sectionally depicted in FIG. 3A. It can be seen that this
embodiment of the forward stop member, when positioned within the
syringe body, defines a radially inward enlargement of a forward
axial portion thereof. Accordingly, instead of inserting the stop
member 80.sub.a into the syringe body, a forward longitudinal
portion of the body could simply be enlarged during its
manufacture.
Alternatively, in conjunction with the modified syringe embodiment
14b illustrated in FIG. 5, inserts such as stop members 80 and
80.sub.a could be replaced by diametrically opposed, inwardly
projecting forward stop portions 94 formed in the sidewall of the
syringe body 42, in a manner similar to that used to form the stop
portions 70 in FIG. 1, and positioned rearwardly of the syringe
body endwall 44 and forwardly of the plunger seal element 66. In
this instance, the pressure absorption zone would be defined by the
interior syringe body volume 96 positioned between the outlet tube
50 and the forward conical face 68 of the plunger seal element 66
when it sealingly engages the forward stop members 94 as depicted
in FIG. 5.
In the previously described embodiments of the improved syringe of
the present invention, the unique pressure absorption zone was
created within the syringe body by forward stop means therein such
as the elements 80, 80.sub.a or 94. However, if desired, such
pressure absorption zone may be formed externally to the syringe
body. Referring now to FIG. 6, an alternate embodiment 10.sub.a of
the syringe and catheter apparatus 10 is illustrated in which a
modified syringe 14.sub.c is provided that is similar in
construction to the previously, described syringes, and has
volume-limiting means such as stops 70 or wall opening 74, but has
removed therefrom the forward stop means. Accordingly, the conical
end surface 68 of the plunger seal element 66 may be forced into
engagement with the complementarily configured interior surface
44.sub.a of the outlet endwall 44.
The external pressure absorption zone is defined by a length of
plastic tubing 96 which has an internal volume equal to the desired
volume of the pressure absorption zone and is interconnectable
between the syringe outlet tube 50 and the catheter inlet fitting
34. Specifically, the tubing 96 has a female inlet fitting 98
adapted to receive the outlet tube 50, and a male discharge fitting
100 adapted for insertion into the gas inlet passage 36 of the
catheter inlet fitting 34. While the plastic tubing 96 is flexible,
when it is operatively interconnected between the syringe and the
catheter as previously described it defines an essentially
inextensible enlargement of the gas-receiving interior of the
catheter. In this manner, when the end face 68 of the plunger seal
element 66 engages the interior surface 44.sub.a of the endwall 44
the 1.5 cc design gas volume will have been forced into the
catheter, but the resulting balloon pressure will be lessened to a
predetermined degree by the pressure absorption zone defined within
the interconnecting tube 96. The syringe 14.sub.c, like the
previously described syringes 14, 14.sub.a and 14.sub.b, is thus
both volume and pressure-limited.
As previously mentioned, the present invention may be conveniently
utilized in conjunction with a gas syringe having a "standard" body
size with a total internal volume in excess of that needed to
provide the catheter with its maximum design volume of gas to fully
inflate its balloon element. By providing the standard syringe body
with appropriate volume-limiting means (such as stops 70 or wall
opening 74) together with the unique pressure reducing means of the
present invention (such as the elements 80, 80.sub.a, 94 or 96) it
may be inexpensively converted to a volume and pressure-limited
syringe such as the syringes 14, 14.sub.a, 14.sub.b and 14.sub.c.
By appropriate correlation between the volume of the pressure
absorption zone, the desired reduction in final balloon pressure
and the rearward spacing of the volume-limiting means, a standard
size syringe body may be conveniently converted for use with
catheters having a variety of maximum gas volume requirements.
However, if desired, the syringe body may be custom sized for each
catheter application so that the necessity for the previously
described volume limiting means is eliminated. This could be
achieved for example, by simply shortening the syringe body length
so that (with the pressure reducing means in place) the resulting
maximum effective available plunger stroke could discharge from the
syringe only the design gas volume of the catheter.
A front end portion of a further alternate embodiment 14d of the
syringe 14 is cross-sectionally illustrated in FIG. 7 and includes
a small disc-shaped orifice plate 102 (see also FIG. 8) having a
small orifice opening 104 extending centrally therethrough. Plate
102 is suitably secured within and extends across the interior of
the syringe outlet tube 50 adjacent its outer end. During an
initial portion of the operation of the modified syringe 14d, the
orifice opening 104 functions to advantageously limit the
pressurization rate of the catheter balloon 30 (FIG. 1) by creating
a significant restriction to gas outflow through outlet tube 50.
While the orifice plate 102 is representatively incorporated for
purposes of illustration in a syringe similar to that shown in FIG.
1, it will be readily appreciated that plate 102, or alternative
orifice-defining means, could also be incorporated in the outlets
of the other syringe embodiments illustrated and described
herein.
To representatively illustrate the operation of the syringe and
catheter apparatus 10 with a conventional syringe, a pressure and
volume-limited syringe such as syringe 14, and the orificed syringe
14.sub.d, three curves 106, 108 and 110 have been plotted on the
graph of FIG. 9. Each of the curves shows the intralumenal pressure
(i.e., the pressure between the catheter balloon and the interior
surface of the artery engaged by the balloon) as a function of time
when each of the three types of syringes was used to inflate the
catheter balloon operatively disposed in an appropriate artery of a
young pig. Curve 106 plots the intralumenal pressure resulting from
the use of a standard syringe, curve 108 resulted from the use of
the pressure and volume-limited syringe 14, and curve 110 resulted
from the use of the orificed syringe 14.sub.d -each syringe being
used, in turn, with the same catheter in the same artery.
It can be seen that the pressure and volume-limited syringe 14
(curve 108) produced a maximum intralumenal pressure that was
approximately half that of the conventional syringe (curve 106),
thus graphically illustrating the considerable safety advantage
afforded by the pressure and volume-limited syringe apparatus of
the present invention.
By comparing curves 106 and 108 it can be seen that the rate of
intralumenal pressure increase during catheter balloon inflation is
rather rapid as illustrated by the nearly vertical left side
portions of curves 106 and 108. In sharp contrast to these rapid
intralumenal pressure rises, the corresponding pressure rise, to
its maximum level, of curve 110 (the orificed syringe 14.sub.d) is
much more gradual, taking approximately 1.5 seconds instead of only
a small fraction of a second as in the case of curves 106 and
108.
This illustrates a further advantage of the orificed syringe
14.sub.d over conventional syringes and, for that matter, over the
pressure and volume limited syringe without the outlet orifice
opening 104 --namely, the maximum intralumenal pressure is
automatically attained in a considerably gentler and slower manner
which is believed to be an even safer catheter balloon inflation
technique.
The comparative syringe test results depicted in FIG. 9 indicate
that the maximum intralumenal pressure attributable to the orificed
syringe 14.sub.d is slightly higher than that resulting when the
non-orificed syringe 14 was used. This is believed to have resulted
from the reduction of the syringe "dead space" volume caused by the
placement therein of the orifice plate 102.
It can be seen that the present invention provides an improved
syringe and catheter apparatus having significantly enhanced
operational safety characteristics. The maximum balloon pressure
achievable with the volume and pressure-limited syringe may be
reduced to a predetermined, safer level without the previous
necessity of utilizing pressure relief valves, external inflatable
elements or other conventional pressure limiting devices which are
subject to wear and/or failure during use. Additionally, other than
the normal necessity of monitoring the oscilloscope for the "wedge"
trace pattern during reinflation of the catheter balloon, there is
no need to otherwise monitor the pressure increase within the
catheter, as with a mechanical pressure gauge, since the maximum
pressure attainable therein is preset, and nonvariable, by virtue
of the unique pressure absorption zone within the apparatus.
While the principles of the present invention are particularly well
adapted for use in conjunction with the illustrated pulmonary
artery catheter, it will be appreciated that such principles may
also be utilized in other gas-operated catheter apparatus such as,
for example, endotracheal catheters which are provided at their
distal ends with inflatable cuff members.
The foregoing detailed description is to be clearly understood as
being given by way of illustration and example only, the spirit and
scope of the present invention being limited solely by the appended
claims.
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